System and method for orthopedic implant configuration

ABSTRACT

Anatomic points within the body are projected outside the body through the use of extenders. The projected points may then be used for measurement, or to facilitate the selection or configuration of an implant that is to be positioned proximate the anatomic points. Such an implant may be a rod for a posterior spinal fusion system. Pedicle screws may be implanted into pedicles of the spine, and may then serve as anchors for the extenders. The extenders may have rod interfaces that receive the rod in a manner that mimics the geometry of the pedicle screws so that the selected or configured contoured rod will properly fit into engagement with the pedicle screws.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 11/178,035, filed Jul. 8, 2005, which claims the benefit of thefiling date of U.S. Provisional Patent Application No. 60/682,344, filedMay 18, 2005, the disclosures of which are hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the selection and/orconfiguration of implantable devices, and more precisely, to posteriorspinal fusion systems.

A wide variety of orthopedic implants exist. Such implants are typicallyanchored to bones within the body. Every person has different bonestructure; accordingly, implants must vary considerably in geometry tomeet the needs of a broad range of patients. Although visualizationmethods such as X-Rays and fluoroscopy can be utilized to help determinebone geometry, contact with the bones must often be made in order toprovide a sufficiently accurate measurement of bony landmarks. Currentprocedures often involve the exposure of a relatively large area topermit such measurement.

According to new minimally invasive surgical (MIS) procedures, manyorthopedic implants can be secured to bone through relatively smallincisions. Unfortunately, if a larger incision must be made to permitbone measurement and implant selection or configuration, most of thebeneficial effects of the MIS implantation procedure will be lost.Accordingly, there is a need in the art for bony landmark measurementand implant selection or configuration methods that can be carried outthrough small incisions. Such methods should be relatively simple andquick to perform, with comparatively simple instrumentation.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1 is a perspective view of two adjacent vertebrae of a spine, withguide wires implanted in the pedicles of the right side.

FIG. 2 is a perspective view of three guide wires in isolation,positioned as though implanted in the pedicles of the right sides ofthree adjacent vertebrae.

FIG. 3 is a perspective view of the guide wires of FIG. 2, with dilatorsadvanced along the guide wires to dilate surrounding tissue.

FIG. 4 is a perspective view the guide wires and dilators of FIG. 3,with cannulas positioned around the dilators.

FIG. 5 is a perspective view of the guide wires and cannulas of FIG. 3,with pedicle screws implanted in the pedicles along the guide wiresthrough the use of an insertion tool.

FIG. 6 is a perspective view of the cannulas and pedicle screws of FIG.5, with extenders positioned in engagement with the cannulas and pediclescrews.

FIG. 7A is a side elevation view of the first cannula, pedicle screw,and extender of FIG. 6.

FIG. 7B is a front elevation view of the first cannula, pedicle screw,and extender of FIG. 6.

FIG. 7C is a front elevation, section view of the first cannula, pediclescrew, and extender of FIG. 6.

FIG. 8 is a perspective view of the cannulas, pedicle screws, andextenders of FIG. 6, with bridges used to keep the extenders in aparallel configuration.

FIG. 9 is a perspective view of the cannulas, pedicle screws, extenders,and bridges of FIG. 8, with a rod seated in the rod interfaces of theextenders for contouring.

FIG. 10 is a perspective view of three adjacent vertebrae of the spine,with the rod secured to the pedicle screws to provide posterior spinalfusion.

FIG. 11 is a perspective view of the guide wires of FIG. 2, with pediclescrews installed and extenders engaging the pedicle screws and guidewires without the use of cannulas, according to one alternative methodof the invention.

FIG. 12 is a perspective view of the pedicle screws and extenders ofFIG. 11, with bridges used to keep the extenders in a parallelconfiguration.

FIG. 13 is a perspective view of the pedicle screws, extenders, andbridges of FIG. 12, with a rod seated in the rod interfaces of theextenders for contouring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to systems and methods for configuringand/or selecting devices to be implanted in the body. Although theexamples provided herein generally relate to contouring a rod for aposterior spinal fusion system, the present invention may be applied toany procedure in which the relative position and/or orientations ofinternal anatomic locations are to be measured or used to configure orselect an implant. Accordingly, the scope of the present invention isnot intended to be limited by the examples discussed herein, but only bythe appended claims.

In this application, an “anatomic point” is a location within the body.An anatomic point need not be located on any specific anatomicstructure. When applied to anatomy, “proximal” refers to a positionrelatively closer to the center of the body, and “distal” refers to aposition relatively further from the center of the body. However, whenreferred to a tool or similar implement, “proximal” refers to a portionrelatively nearer the operator of the tool or similar implement, and“distal” refers to a portion relatively further from the operator.

The phrase “spatial transformation” refers to any mathematical procedurein which one or more coordinates can be transformed in a manner thatpermits the original coordinates to be determined based on the resultsof the transformation. Accordingly, a spatial transformation may involveany combination of translation and rotation of the original coordinates,as long as the transformation can be analytically reversed to permit theoriginal coordinates to be obtained. A “translational spatialtransformation” is a spatial transformation in which the originalcoordinates are all uniformly translated along the same vector.

The term “mate” refers to any type of connection in which cooperatingfeatures engage each other to restrict relative motion of the matingparts. The term “couple” is not limited to fixed attachment, but alsoincludes sliding attachment and the like. The term “receive” does notrequire one item to completely capture another; rather, one itemreceives another if the first item engages the second item in a mannerthat restricts relative motion of the items.

Referring to FIG. 1, a perspective view illustrates a portion of a spine10. FIG. 1 illustrates only the bony structures; accordingly, ligaments,cartilage, and other soft tissues are omitted for clarity. The spine 10has a cephalad direction 12, a caudal direction 14, an anteriordirection 16, a posterior direction 18, and a medial/lateral axis 20,all of which are oriented as shown by the arrows bearing the samereference numerals. In this application, “left” and “right” are usedwith reference to a posterior view, i.e., a view from behind the spine10. “Medial” refers to a position or orientation toward a sagittal plane(i.e., plane of symmetry that separates left and right sides from eachother) of the spine 10, and “lateral” refers to a position ororientation relatively further from the sagittal plane.

As shown, the portion of the spine 10 illustrated in

FIG. 1 includes a first vertebra 24, which may be the L5 (Fifth Lumbar)vertebra of a patient, and a second vertebra 26, which may be the L4(Fourth Lumbar) vertebra of the patient. The systems and methods may beapplicable to any vertebra or vertebrae of the spine 10 and/or thesacrum (not shown). In this application, the term “vertebra” may bebroadly interpreted to include the sacrum.

As shown, the first vertebra 24 has a body 28 with a generally disc-likeshape and two pedicles 30 that extend posteriorly from the body 28. Aposterior arch, or lamina 32, extends between the posterior ends of thepedicles 30 to couple the pedicles 30 together. The first vertebra 24also has a pair of transverse processes 34 that extend laterally fromthe pedicles 30 generally along the medial/lateral axis 20, and aspinous process 36 that extends from the lamina 32 along the posteriordirection 18.

The first vertebra 24 also has a pair of superior facets 38, which arepositioned toward the top of the first vertebra 24 and face generallymedially. Additionally, the first vertebra 24 has inferior facets 40,which are positioned toward the bottom of the first vertebra 24 and facegenerally laterally. Each of the pedicles 30 of the first vertebra 24has a saddle point 42, which is positioned generally at the center ofthe juncture of each superior facet 38 with the adjacent transverseprocess 34.

Similarly, the second vertebra 26 has a body 48 from which two pedicles50 extend posteriorly. A posterior arch, or lamina 52, extends betweenthe posterior ends of the pedicles 50 to couple the pedicles 50together. The second vertebra 26 also has a pair of transverse processes54, each of which extends from the corresponding pedicle 50 generallyalong the medial/lateral axis 20, and a spinous process 56 that extendsfrom the lamina 52 along the posterior direction 18.

The second vertebra 26 also has a pair of superior facets 58, which arepositioned toward the top of the second vertebra 26 and face generallyinward. Additionally, the second vertebra 26 has inferior facets 60,which are positioned toward the bottom of the second vertebra 26 andface generally outward. Each of the pedicles 60 of the second vertebra26 has a saddle point 62, which is positioned generally at the center ofthe juncture of each superior facet 58 with the adjacent transverseprocess 54.

The superior facets 38 of the first vertebra 24 articulate (i.e., slideand/or press) with the inferior facets 60 of the second vertebra 26 tolimit relative motion between the first and second vertebrae 24, 26.Thus, the combination of each superior facet 38 with the adjacentinferior facet 60 provides a facet joint 64. The first and secondvertebrae 24, thus define two facet joints 64 that span the distancebetween the first and second vertebrae 24, 26. The inferior facets 40 ofthe first vertebra 40 and the superior facets 58 of the second vertebra26 are part of other facet joints that control motion between the firstand second vertebrae 24, 26 and adjacent vertebrae (not shown) and/orthe sacrum (also not shown).

The vertebrae 24, 26 and/or the intervertebral disc (not shown) betweenthem, may be damaged or diseased in some manner that makes it desirableto secure the vertebrae 24, 26 together in a manner that preventsrelative motion between them. Accordingly, posterior spinal fusion maybe employed to secure the pedicles 30, 50 together. FIGS. 1 through 10illustrate one method of configuring and installing a posterior spinalfusion system. FIGS. 11 through 13 illustrate steps that may be employedin place of the steps of FIGS. 6 through 9.

As further illustrated in FIG. 1, a first guide wire 70 has beeninserted into the right-side pedicle 30 of the first vertebra 24, and asecond guide wire 72 has been inserted into the right-side pedicle 50 ofthe second vertebra 26. The guide wires 70, 72 pass through the saddlepoints 42, 62, respectively, of the pedicles 30, 50. Each of the guidewires 70, 72 has a proximal end 74 and a distal end 76. As shown, theproximal ends 74 are exposed, and the distal ends 76 are implanted inthe pedicles 30, 50. The distal ends 76 may be implanted by methodsknown in the surgical arts.

Referring to FIG. 2, a perspective view illustrates the first and secondguide wires 70, 72 of FIG. 1, with the vertebrae 24, 26 removed forclarity. A third guide wire 78 is also shown. The third guide wire 78 ispositioned adjacent to the first and second guide wires 70, 72 as thoughthe third guide wire 78 were implanted in the right-hand pedicle of avertebra (not shown) directly superior to the second vertebra 26.Accordingly, the method of FIGS. 1 through 10 may be used to securetogether vertebrae on multiple levels, not just two adjacent vertebrae.

Referring to FIG. 3, a perspective view illustrates the guide wires 70,72, 78, in conjunction with a first dilator 80, a second dilator 82, anda third dilator 88. Each of the dilators 80, 82, 88 has a proximal end92 and a distal end 94. The proximal ends 92 may be shaped for grippingby hand, or for attachment to a handle or the like. The distal ends 94are rounded to permit relatively gentle spreading of tissues surroundingthe guide wires 70, 72, 78 by the dilators 80, 82, 88.

Each of the dilators 80, 82, 88 has a bore sized to receive the proximalend 74 of the corresponding guide wire 70, 72, or 78, so that thedilators 80, 82, 88 are able to slide along the guide wires 70, 72, 78toward the distal ends 74, thereby spreading the tissues away from theguide wires 70, 72, 78. As an alternative to the guide wires 70, 72, 78and the dilators 80, 82, 88, a variety of other guiding devices and/ordilation devices may be used within the scope of the present invention.

Referring to FIG. 4, a perspective view illustrates the guide wires 70,72, 78 and dilators 80, 82, 88, with the addition of a first cannula100, a second cannula 102, and a third cannula 108. Each of the cannulas100, 102, 108 has a proximal end 112, a distal end 114, with a borepassing between the proximal and distal ends 112, 114. Each proximal end112 has a port 116 in communication with the bore, and a tab 118 thatmay facilitate manipulation or securement of the corresponding cannula100, 102, or 108.

Each distal end 114 has a taper 122 that provides a reduction in thediameter of the cannula 100, 102, or 108 toward the distal end 114.Additionally, each distal end 114 has a pair of arms 124 that extendgenerally parallel to the axis of the corresponding cannula 100, 102, or108. The arms 124 define a first slot 126 and a second slot 128 thatalso extend parallel to the axis of the corresponding cannula 100, 102,108. The ends of the arms 124 define a port 130 that also communicateswith the bore of the cannula 100, 102, or 108.

The cannulas 100, 102, 108 are inserted around the guide wires 70, 72,78. The cannulas 100, 102, 108 may be placed by withdrawing dilators 80,82, 88, inserting the cannulas 100, 102, 108 around the proximal ends 74of the guide wires 70, 72, 78, inserting the distal ends 94 of thedilators 80, 82, 88 into the ports 116 of the proximal end 112 of thecannulas 100, 102, 108, and then advancing the dilators 80, 82, 88 alongthe guide wires 70, 72, 78 to urge the cannulas 100, 102, 108 toward thedistal ends 76 of the guide wires 70, 72, 78, into the dilated tissue.

According to one alternative method, the dilators 80, 82, 88 are removedto permit placement of the cannulas 100, 102, 108, and are notre-inserted. According to other alternative embodiments, cannulas (notshown) may be modular, or may have dilatable distal ends that enableplacement of the cannulas around the dilators 80, 82, 88, so that thedilators 80, 82, 88 need not be removed from the guide wires 70, 72, 78until the cannulas are properly positioned. The present invention is notlimited to use of cannulas like those of

FIG. 4; rather, any of a variety of cannulas may be used.

Referring to FIG. 5, a perspective view illustrates the guide wires 70,72, 78 and cannulas 100, 102, 108, with the addition of connectionelements designed to be retained at the distal ends 114 of the cannulas100, 102, 108. The connection elements may be fixation members designedto anchor a rod to the first vertebra 24, the second vertebra 26, andthe third vertebra (not shown in FIG. 5). More precisely, the connectionelements may be pedicle screws 140, 142, and 148 implantable invertebral pedicles.

The pedicle screws 140, 142, 148 may be designed to provide polyaxialcoupling to the associated pedicles. Each of the pedicle screws 140,142, 148 has a cage 152 shaped to receive a rod, and a screw 154 thatpasses through an aperture (not visible) of the cage 152 in such amanner that the screw 154 is able to extend from the cage 152 along aplurality of relative orientations. Thus, after the screw 154 has beenimplanted in a pedicle, the orientation of the cage 152 with respect tothe screw 154 can still be altered. Each of the screws 154 has a lumenpassing along the axis of the screw 154 so that the screws 154 can slidealong the guide wires 70, 72, 78 for accurate implantation in thepedicles.

Each cage 152 has two arms 156 that extend generally away from the screw154 and define a first slot 158 and a second slot 160 through which arod (not shown in FIG. 5) can pass. The closed ends of the slots 158,160 are rounded in a manner that corresponds to the radius of the rod tobe retained within the cage 152 to facilitate secure retention of therod. The inward-facing surfaces of the arms 156 may be threaded toenable the arms 156 may be threaded to enable the arms 156 to receive anut (not shown in FIG. 5). Tightening of the nut then presses the rodagainst the head (not shown) of the screw 154 to keep the rod in placewithin the slots 158, 160, and to lock the orientation of the screw 154with respect to the cage 152.

The pedicle screws 140, 142, 148 represent only one of many types ofconnection elements that may be used in connection with the presentinvention. A variety of known devices may be used to secure a rod to aplurality of vertebra to provide posterior fusion.

Upon implantation in the pedicles, the pedicle screws 140, 142, 148 arepositioned such that a first anatomic point 164, a second anatomic point166, and a third anatomic point 168 are within the cages 152 of thefirst pedicle screw 140, the second pedicle screw 142, and the thirdpedicle screw 148, respectively. Upon installation of the rod, the axisof the rod is to pass through the anatomic points 164, 166, 168.

The pedicle screws 140, 142, 148 may be installed in a variety of ways.According to one method, the dilators 80, 82, 88 are first removed.Then, each of the pedicle screws 140, 142, 148 is implanted through theuse of an insertion tool 170. The insertion tool 170 has a handle 172designed to be gripped by hand, and a stem 174 extending from the handle172. The stem 174 has a distal end 176 shaped to engage the head of eachof the screws 154. According to one example, the head of each of thescrews 154 has a hexagonal recess (not visible), and the distal end 176has a corresponding hexagonal male feature (not visible). Thus, torqueapplied to the handle 172 can be transmitted to each of the screws 154.

The stem 174 also has a lumen (not shown) sized to fit around each ofthe guide wires 70, 72, 78 so that the guide wires 70, 72, 78 can beused to guide implantation of the screws 154 through the use of theinsertion tool 170. Slots 178 provide access to the lumen for cleaning.

Each of the screws 154 is coupled to the insertion tool 170 byconnecting the head of the screw 154 to the distal end 176 of the stem174. The insertion tool 170 is then moved to insert the proximal end 74of the corresponding guide wire 70, 72, 78 through the lumen of thescrew 154 and into the lumen of the stem 174. The insertion tool 170 isused to insert the pedicle screw 140, 142, or 148 through thecorresponding cannula 100, 102, or 108 until the screw 154 contacts thefirst pedicle 30, the second pedicle 50, or the third pedicle. Then,torque and axial pressure are applied to the handle 172 to embed thethreads of the screw 154 into the bone. The same method may be used toimplant all three of the pedicle screws 140, 142, 148. After the pediclescrews 140, 142, 148 have been implanted, the guide wires 70, 72, 78 maybe removed.

The cages 152 may be sized to fit relatively snugly within the ports 130at the distal ends 114 of the cannulas 100, 102, 108. The arms 124 ofeach distal end 114 thus form a docking feature that enables thecorresponding pedicle screw 140, 142, or 148 to dock with the distal end114 of the corresponding cannula 100, 102, 108. The cages 152 are thenconstrained to be coaxial with the cannulas 100, 102, 108.

Referring to FIG. 6, a perspective illustrates the cannulas 100, 102,108 and the pedicle screws 140, 142, 148 of FIG. 5, with a firstextender 180, a second extender 182, and a third extender 188 insertedinto engagement with the cannulas 100, 102, 108 and pedicle screws 140,142, 148. The extenders 180, 182, 188 are used to project the anatomicpoints 164, 166, 168 outside the patient's body to facilitate propercontouring of the rod (not shown in FIG. 6). Thus, the space between thecannulas 100, 102, 108 need not be accessed to obtain the proper rodconfiguration.

In the embodiment of FIG. 6, each of the extenders 180, 182, 188 has aproximal portion 192, a distal portion 194, and a stem 196 extendingbetween the proximal and distal portions 192, 194. The proximal portion192 of each of the extenders 180, 182, 188 has a handle 198 that may begrasped by hand or by a tool. Additionally, each proximal portion 192has an implant interface, which may take the form of a rod interface200. Each rod interface 200 is shaped to receive a portion of a rod tofacilitate contouring of the rod so that the contoured rod will passthrough the anatomic points 164, 166, 168 within the cages 152 of theimplanted pedicle screws 140, 142, 148.

Each of the rod interfaces 200 has two arms 202 that extend generallyaway from the remainder of the corresponding extender 180, 182, or 188.The arms 202 of each rod interface 200 define a trough 204 through whicha rod (not shown in FIG. 5) can pass. The base of the trough 204 isrounded in a manner that corresponds to the radius of the rod to beretained within the cage 152 to facilitate secure retention of the rod.The arms 202 are similar in configuration to the arms 156 of the cage152 of the corresponding pedicle screw 140, 142, 148, and the trough 204is similar to a trough defined by the first and second slots 158, 160 ofthe cage 152. Accordingly, the rod interfaces 200 mimic the geometry ofthe cages 152 of the pedicle screws 140, 142, 148.

The distal portion 194 of each of the extenders 180, 182, 188 has adocking element 208 that may be used to facilitate engagement andrelative orientation of the extenders 180, 182, 188 with the cages 152of the pedicle screws 140, 142, 148. Each docking element 208 mayinclude an axial stud 210 that extends along the axis of the extender180, 182, or 188, and a transverse stud 212 proximate the distal end ofthe axial stud 210, that extends perpendicular to the axis of theextender 180, 182, or 188.

The extenders 180, 182, 188 represent only one of many potentialextender configurations that may be used in connection with the presentinvention. Other extender configurations may be advantageous,particularly if the cannulas, dilators, connection elements, or guidancemembers employed are different from those of FIG. 6.

Alternatively, rather than providing an implant interface, extendersaccording to the invention may simply be used to provide a numericmeasurement of relative positions or orientations of the correspondinganatomic points. Extenders may thus be incorporated into one or moremeasurement instruments (not shown). For example, extenders may registeron the pedicle screws 140, 142, 148 and may be coupled to a series ofsliders and/or rotary elements that provide linear and/or rotarymeasurements of the relative positions of the cages 152. Suchmeasurements may be used to configure or select an implant. According toone example, such a measurement instrument may measure displacementsbetween all three of the implanted cages 152 to provide a triangle, twosides of which define the path that should be followed by the axis ofthe rod.

Returning the configuration of FIG. 6, when the extenders 180, 182, 188are inserted into the cannulas 100, 102, 108, the transverse studs 212slide into the corresponding cages 152. The transverse stud 212simulates a portion of the rod that will ultimately be retained in thecages 152; thus, the transverse stud 212 may fit relatively snuglywithin the corresponding cage 152. The ends of each transverse stud 212may extend through the first and second slots 158, 160 of thecorresponding cage 152 to restrict relative rotation between the cage152 and the extender 180, 182, 188. If desired, the axial stud 210 maybe sized to have relatively little clearance with the inward-facingsurfaces of the arms 156 of the cage 152 so that the extenders 180, 182,188 are constrained to remain coaxial with the cages 152. Further, theaxial stud 210 may have exterior threads that threadably engage thethreads on the inward-facing surfaces of the arms 156 of thecorresponding cage 152.

Whether or not full axial constraint is achieved by engagement of theaxial stud 210 and the transverse stud 212 with the cage 152, thecannulas 100, 102, 108 may receive the stems 196 of the extenders 180,182, 188 with relatively little clearance such that each extender 180,182, 188 is constrained to be coaxial with the corresponding cannula100, 102, 108. Since the distal ends 114 of the cannulas 100, 102, 108are docked with the cages 152, the cannulas 100, 102, 108 are coaxialwith the cages 152, and the extenders 180, 182, 188 are coaxial with thecannulas 100, 102, 108 and the cages 152.

The coaxiality of the extenders 180, 182, 188 with the cages 152 enablesthe rod interfaces 200 to provide a linear transformation of each of thefirst, second, and third anatomic points 164, 166, 168 to points outsidethe body. More precisely, the first extender 180 projects the firstanatomic point 164 along the length of the first extender 180 to a firstprojected point 214 within the rod interface 200 of the first extender.The second and third anatomic points 166, 168 are similarly projected tosecond and third projected points 216, 218. However, since the extenders180, 182, 188 are not parallel to each other, the projected points 214,216, 218 do not have the same spatial relationship (i.e., relativepositioning) as the anatomic points 164, 166, 168.

Referring to FIG. 7A, a side elevation view illustrates the firstcannula 100, the first pedicle screw 140, and the first extender 180 ofFIG. 6. As shown, the ends of the transverse stud 212 of the firstextender 180 may extend through the first and second slots 126, 128 ofthe distal end 114 of the first cannula 100 as well as through the firstand second slots 158, 160 of the cage 152 of the first pedicle screw140.

Referring to FIG. 7B, a front elevation view illustrates the firstcannula 100, the first pedicle screw 140, and the first extender 180 ofFIG. 6. FIG. 7B provides an end view of the transverse stud 212,illustrating how it engages the first and second slots 126, 128 of thedistal end 114 of the first cannula 100 and the first and second slots158, 160 of the cage 152 of the first pedicle screw 140.

Referring to FIG. 7C, a front elevation, section view illustrates thefirst cannula 100, the first pedicle screw 140, and the first extender180 of FIG. 6. As shown, the first extender 180 may include two separateparts: a central member 220 and a sleeve member 222. The sleeve member222 has a countersink 224 at the proximal portion 192, a taper 226 atthe distal portion 194, and a lumen 228 extending between the proximaland distal portions 192, 194 to receive the central member 220.

The central member 220 may include an enlarged head 234 that fits withinthe countersink 224 of the sleeve member 222, a stem 238 that extendsthrough the lumen 228 of the sleeve member 222, and a lumen 240 thatpasses through the stem 238. The lumen 228 is optional, and may be usedto receive the first guide wire 70, particularly for the implantationmethod that will be set forth in connection with FIGS. 11, 12, and 13.For the present method, the lumen 228 may optionally be omitted becausethe guide wires 70, 72, 78 may be removed prior to insertion of theextenders 180, 182, 188.

Usage of two separate members to provide each of the extenders 180, 182,188 enables the transverse studs 212 to be seated within the first andsecond slots 158, 160 of each cage 152 while the sleeve members 222 arerotated axially to threadably engage the axial studs 210 with theinward-facing surfaces of the arms 156 of the cages. The sleeve members222 may be rotated until they press the corresponding transverse studs212 into the first and second slots 158, 160 of the cages 152. Thetransverse studs 212 are then seated tightly within the cages 152 in amanner that very closely simulates the ultimate position of the rod.

Referring to FIG. 8, a perspective view illustrates the cannulas 100,102, 108, pedicle screws 140, 142, 148, and extenders 180, 182, 188 ofFIG. 6, with the addition of a first bridge 250 and a second bridge 252.The bridges 250, 252 are used to keep the extenders 180, 182, 188substantially parallel to each other to constrain the spatialtransformation of the anatomic points 164, 166, 168. The bridges 250,252 are designed to constrain the extenders 180, 182, 188 only toparallelism. Thus, the bridges 250, 252 do not limit relativetranslation or relative axial rotation of the extenders 180, 182, 188.

Each of the first and second bridges 250, 252 has a first slider 254 anda second slider 256. The first slider 254 of each of the bridges 250,252 has a pair of grooves 258 that face inward. The second slider 256 ofeach of the bridges 250, 252 has a pair of flanges 260 that extendoutward into the grooves 258 of the corresponding first slider 254 sothat the first and second sliders 254, 256 are linearly slidablerelative to each other to permit lengthening or shortening of thebridges 250, 252. Each of the sliders 254, 256 also has an aperture 262that fits around the enlarged head 234 of the central member 220 of thecorresponding extender 180, 182, or 188. The apertures 262 are sized tofit around the enlarged heads 234 with relatively little clearance sothat the bridges 250, 252 keep the extenders 180, 182, 188 parallel toeach other without restricting relative axial rotation.

The bridges 250, 252 embody only one of many possible configurationsthat may be used in connection with the invention. According to onealternative embodiment (not shown), each bridge does not have twosliders, but has two members that are rotatably coupled to each other.Each of the members has an aperture like the apertures 262 of thebridges 250, 252, so that the bridges can permit relatively freerelative translation and axial rotation of the extenders 180, 182, 188,while keeping the extenders 180, 182, 188 parallel to each other. Thebridges would simply elongate and contract through the use of rotarymotion instead of linear motion.

Returning to the configuration of FIG. 8, once the bridges 250, 252 havebeen applied, the extenders 180, 182, 188 are parallel. The projectedpoints 214, 216, 218 then mimic the relative positioning of the anatomicpoints 164, 166, 168 within the body. Thus, the extenders 180, 182, 188apply a translational spatial transformation to the anatomic points 164,166, 168 to move them to a more accessible location without alteringtheir positions relative to each other. Accordingly, a rod contouredsuch that its axis passes through the projected points 214, 216, 218 maybe installed such that its axis passes through the anatomic points 164,166, 168 to properly extend through the cages 152 of the pedicle screws140, 142, 148.

Referring to FIG. 9, a perspective view illustrates the cannulas 100,102, 108, the pedicle screws 140, 142, 148, the extenders 180, 182, 188,and the bridges 250, 252 of FIG. 8, with a rod 270 seated in the rodinterfaces 200 of the extenders 180, 182, 188 for contouring. The rod270 has a first end 272, a second end 274, and a central portion 276. Asshown, the first end 272 is positioned in the rod interface 200 of thefirst extender 180, the central portion 276 is positioned in the rodinterface 200 of the second extender 182, and the second end 274 ispositioned in the rod interface 200 of the third extender 188.

Due to natural variations in spinal morphology, the cages 152 of thepedicle screws 140, 142, 148 may not be arranged in a straight line.Thus, the rod interfaces 200 may not be arranged in a straight line.Thus, the rod 270 may need to be bent into the proper shape, forexample, through the use of tooling such as pliers, a vice, or the like,so that it will lie properly within the rod interfaces 200. The processof deforming the rod 270 to the required shape may be termed“contouring.”

Contouring may be carried out by, first, placing the undeformed rod 270in the rod interfaces 200 to determine how the rod 270 should bedeformed to lie properly within the rod interfaces 200. Then, the rod270 is deformed, and again placed in the rod interfaces 200 to check thefit. This process is repeated until the rod 270 is shaped to provide anoptimal fit with the rod interfaces 200.

In the alternative to contouring, the rod 270 may simply be selectedfrom a kit or the like. For example, such a kit (not shown) may includerods bent at a variety of angles. The rod interfaces 200 could be usedto select the proper rod from the kit by placing each rod, in turn, onthe rod interfaces 200 until one is identified that has the proper fit.As another alternative, the rod 270 may be custom fabricated, forexample, by measuring the relative positions of the rod interfaces 200and using a CNC procedure to form the rod 270.

After the rod 270 has been configured or selected, the rod 270 and theextenders 180, 182, 188 may be removed from the operating site, leavingthe pedicle screws 140, 142, 148 in place. The cannulas 100, 102, 108may also be removed at this stage, depending on the method that will beused to implant the rod 270. The rod 270 may be inserted subcutaneouslyand placed on the cages 152 by making additional incisions to connectthe access passageways provided by the cannulas 100, 102, 108.Alternatively, MIS (Minimally Invasive Surgical) techniques may be usedto implant the rod 270 without making additional major incisions, forexample, by inserting the rod 270 through the slots 126, 128 of thedistal ends 114 of the cannulas 100, 102, 108.

Referring to FIG. 10, a perspective view illustrates the completedposterior spinal fusion system. In addition to the first and secondvertebrae 24, 26, FIG. 10 illustrates a third vertebra 278 superior tothe second vertebra 26. The third vertebra 278 has features similar tothose set forth in the description of the first and second vertebrae 24,26. Most pertinently, the third vertebra 278 has pedicles 280 withsaddle points 282.

As shown, the first pedicle screw 140 is implanted in the pedicle 30 ofthe right side of the first vertebra 24, the second pedicle screw 142 isimplanted in the pedicle 50 of the right side of the second vertebra 26,and the third pedicle screw 148 is implanted in the pedicle 280 of theright side of the third vertebra 278. The rod 270 passes through theslots 158, 160 of the cages 152 in such a manner that the axis (notshown) of the rod 270 passes through the anatomic points 164, 166, 168.

First, second, and third nuts 290, 292, 298 have been rotated intoengagement with the inward-facing surfaces of the arms 156 of the cages152 of the first, second, and third pedicle screws 140, 142, 148,respectively. The nuts 290, 292, 298 have been tightened to press thefirst end 272, central portion 276, and second end 274, respectively,against the heads of the screws 154 of the pedicle screws 140, 142, 148,respectively. Thus, the cages 152 are no longer freely rotatable withrespect to the screws 154, but are instead locked in their currentorientations.

The pedicle screws 140, 142, 148 thus cooperate with the rod 270 torestrict relative motion of the vertebrae 24, 26, 278 to form aposterior vertebral fusion system. If desired, a similar system may beimplanted in the left-side pedicles 30, 50, 280 of the vertebrae 24, 26,278 through the method set forth previously to provide a bilateralsystem. Additionally, the present invention is not limited to athree-level fusion system, but may be used to fuse any number ofvertebrae together. To fuse more than three vertebrae together, thesteps set forth above may simply be repeated for each additionalvertebra, and the rod may be placed on four or more rod interfaces forconfiguration or selection.

The foregoing is only one of many methods encompassed within the scopeof the present invention. According to one alternative method, thecannulas 100, 102, 108 may be omitted entirely from the procedure. Sucha method may commence with the steps outlined above in the descriptionsof FIGS. 1, 2, and 3, but may then include the steps illustrated inFIGS. 11, 12, and 13.

Referring to FIG. 11, a perspective view illustrates the guide wires 70,72, 78 of FIG. 2, with the pedicle screws 140, 142, 148 and extenders180, 182, 188 installed. From the step of FIG. 3, the dilators 80, 82,88 may be removed, and the distal ends of the extenders 180, 182, 188may be mated to the pedicle screws 140, 142, 148. More precisely, thetransverse studs 212 may be inserted into the slots 158, 160, and theaxial studs 210 may be threadably engaged with the inward-facingsurfaces of the arms 156 in the manner set forth previously.

Then, the extenders 180, 182, 188 may be used as insertion tools toimplant the pedicle screws 140, 142, 148 in the pedicles 30, 50, 280.More precisely, the extenders 180, 182, 188 are positioned to insert theproximal ends 74 of the guide wires 70, 72, 78 through the pediclescrews 140, 142, 148, and into the lumens 240 of the central members 220of the extenders 180, 182, 188. The extenders 180, 182, 188 are advanceduntil the screws 154 contact the pedicles 30, 50, 280, and then theextenders 180, 182, 188 are subjected to torque and axial pressure,which may be applied to the handles 198, to implant the screws 154 inthe pedicles 30, 50, 280. The guide wires 70, 72, 78 may sufficientlyguide implantation of the pedicle screws 140, 142, 148 without requiringthe use of the cannulas 100, 102, 108.

In the alternative to the above, the insertion tool 170 may be used inthe manner described previously to implant the pedicle screws 140, 142,148, without the use of the cannulas 100, 102, 108. The distal portions194 of the extenders 180, 182, 188 may then be mated to the cages 152 asset forth above, after implantation of the pedicle screws 140, 142, 148.

Referring to FIG. 12, a perspective view illustrates the pedicle screws140, 142, 148 and the extenders 180, 182, 188, with the addition of thebridges 250, 252. As described in connection with FIG. 8, the bridges250, 252 are applied to constrain the extenders 180, 182, 188 toparallel orientations.

Referring to FIG. 13, a perspective view illustrates the pedicle screws140, 142, 148, the extenders 180, 182, 188, and the bridges 250, 252,with the rod 270 seated in the rod interfaces 200 of the extenders 180,182, 188 for contouring. As described in connection with FIG. 9, the rod270 may be configured or selected by placing it in the rod interfaces200 to ensure that it will fit properly in the cages 152 of the pediclescrews 140, 142, 148 upon implantation. After the rod 270 has beenconfigured or selected, the additional steps set forth in thedescription of FIG. 9 (aside from removal of the cannulas 100, 102, 108)may be followed to obtain the fully implanted and assembled posteriorspinal fusion system illustrated in FIG. 10.

The foregoing description discloses a number of different elements, anyof which may be components of a system for configuring or selecting oneor more implants for implantation in a body of a patient. Although theforegoing examples relate to the assembly and implantation of aposterior spinal fusion system, the present invention may be applied toa wide variety of implants, within and outside the orthopedic area. Thepresent invention has particular benefits when an implant is to beconfigured or selected for a given patient, with reference to two ormore anatomic points within the body.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. It isappreciated that various features of the systems and methods describedabove can be mixed and matched to form a variety of other alternatives.As such the described embodiments are to be considered in all respectsonly as illustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1. A method for configuring or selecting one or more implants forimplantation in a body of a patient, the method comprising: positioninga distal portion of a first extender proximate a first anatomic pointwithin the body, through which the one or more implants are to pass;positioning a distal portion of a second extender proximate a secondanatomic point within the body, through which the one or more implantsare to pass; constraining an orientation of the first extender withrespect to the second extender to provide a spatial transformation ofthe first and second anatomic points to first and second projectedpoints outside the body; and configuring or selecting the one or moreimplants based on locations of the first and second projected points. 2.The method of claim 1, wherein the first anatomic point is proximate afirst pedicle of the spine and the second anatomic point is proximate asecond pedicle of the spine, the method further comprising implantingthe one or more implants proximate the spine.
 3. The method of claim 2,wherein the one or more implants comprise a rod for a posterior spinalfusion system, wherein implanting the one or more implants proximate thespine comprises securing the rod to a plurality of vertebrae of thespine to restrict relative motion of the vertebrae.
 4. The method ofclaim 3, wherein positioning the distal portion of the first extenderproximate the first anatomic point comprises mating the distal portionof the first extender with a rod interface of a first fixation memberimplantable in the first pedicle, wherein positioning the distal portionof the second extender proximate the second anatomic point comprisesmating the distal portion of the second extender with a rod interface ofa second fixation member implantable in the second pedicle.
 5. Themethod of claim 3, wherein configuring or selecting the one or moreimplants based on locations of the first and second projected pointscomprises receiving the rod with proximal portions of the first andsecond extenders.
 6. The method of claim 1, wherein constraining theorientation of the first extender with respect to the second extendercomprises coupling a first bridge to the first and second extenders tokeep the first and second extenders parallel to each other whilepermitting substantially free relative translation between the first andsecond extenders.
 7. The method of claim 1, further comprising:positioning a distal portion of a third extender proximate a thirdanatomic point within the body, through which the one or more implantsare to pass; and constraining an orientation of the second extender withrespect to the third extender such that the method provides a spatialtransformation of the first, second, and third anatomic points to first,second, and third projected points outside the body.